To see wildlife in the Triangle, sometimes you need go no further than your own backyard. A new study helps explain why some animals are sometimes more often found in suburban areas than wild ones: because people are feeding them - sometimes accidentally - and to a lesser degree, providing them with shelter.
"They're using the gardens a little bit, they're using the brush piles a little bit, and they're using the water features, but feeding has the most dramatic influence on animal activity in the backyard," said Roland Kays, research associate professor at North Carolina State University and director of the Biodiversity & Earth Observation Lab at the NC Museum of Natural Resources.
The study, published in Frontiers in Ecology and Evolution, was designed to understand what scientists call the "urban wildlife paradox." While scientists know human development generally causes biodiversity loss, they've also found that moderately developed areas can have an abundance and variety of mammals compared with wild areas.
"There's this idea that nature and humans don't coexist well," Kays said. "But what we've been finding is that when it comes to mammals, especially in North America, they actually do pretty well around people. You end up with high abundance. You expect there to be fewer animals, and there's actually more."
Researchers wanted to know why that is. To test whether food and shelter are attracting animals, researchers set up cameras in the backyards of 58 homes near Raleigh, Durham, and outside of Chapel Hill, as well as in nearby forests in rural and urban areas nearby for comparison. The study was conducted in collaboration with scientists at the University of Montana.
By analyzing the pictures they found, researchers discovered seven species -squirrels, gray and red fox, Virginia opossum, eastern cottontail rabbits, woodchucks and eastern chipmunks - were more frequently seen in yards compared to forests. Eleven species, such as white-tailed deer, squirrels and raccoons, were more common in suburban forests compared to rural ones.
"This basically confirmed the urban-wildlife paradox, showing that some species are more abundant in yards," Kays said. "It's not a big surprise if you live in the suburbs - you see the animals. It's the squirrels, raccoons, deer and opossum."
Feeding animals - mainly at birdfeeders - had the strongest impact on the abundance of animals in a yard. Eastern gray squirrels were the most common sight at feeders. They were more common at feeders than in suburban or rural forests. Other common species at feeders were cottontail rabbits, raccoons and opossums.
"This supports the idea that direct human subsidies are a big part of the explanation for the urban-wildlife paradox," Kays said. "It shows that individual decisions by homeowners and private property owners can have a big impact on the wildlife in the backyard and living in the area."
Predators such as coyotes and foxes were slightly more common in yards when other prey animals, such as squirrels or rabbits, were more abundant. However, the effect wasn't strong - the researchers said it would take the number of prey to increase by 713 times to double the number of predators in the yard. They only observed one coyote and one red fox eating compost.
"There was some attraction to prey, but it was a pretty small effect," Kays said.
Meanwhile, fences were deterrents to fox and other predators, and pets were deterrents to opossums and raccoons.
Kays said the findings raise questions about what homeowners should do, and whether attracting wildlife is good or bad.
"You see widespread recommendations: Don't feed the bears. Where do you draw the line from small birds to squirrels, rabbits and raccoons? When does it become bad to feed the animals, even if you're doing it accidentally?" Kays said. "On one hand many people enjoy having wildlife around and they can help support a healthy local ecosystem; however, they could cause conflict with people."
The study, "Does Use of Backyard Resources Explain the Abundance of Urban Wildlife?" was published Oct. 26 in the journal Frontiers in Ecology and Evolution. The paper's lead author was Christopher P. Hansen of the Wildlife Biology Program in the Franke College of Forestry and Conversation at the University of Montana. Co-authors include Arielle W. Parsons and Roland Kays of NC State and Joshua Millspaugh of the University of Montana. The research was supported by the National Science Foundation under grant No. 1539622.
Note to editors: The abstract follows.
"Does Use of Backyard Resources Explain the Abundance of Urban Wildlife?"
Authors: Christopher P. Hansen of the University of Montana, Arielle W. Parsons and Roland Kays of NC State and Joshua J. Millspaugh of the University of Montana.
Published: Online in Frontiers in Ecology and Evolution. Oct. 26, 2020.
Abstract: While urbanization is clearly contributing to biodiversity loss, certain wildlife assemblages can paradoxically be diverse and abundant in moderately developed areas. One hypothesis to explain this phenomenon is that abundant anthropogenic resources for wildlife (i.e. food and shelter) outweigh the costs associated with urbanization. To test this hypothesis, we used camera traps to measure mammal species richness, diversity, and relative abundance (i.e., detection rate) in 58 residential yards in Raleigh, North Carolina, focusing on six types of features that might be used as resources: animal feeding, vegetable gardens, compost piles, chicken coops, brush piles, and water sources. We also placed cameras at random control sites within each yard and sampled forests in nearby suburban and rural areas for comparison. We fit mixed-effects Poisson models to determine whether yard features, yard-scale characteristics, or landscape-scale landcover predicted mammal relative abundance for eight species. We also tested if the relative abundance of native canid predators in yards was related to the number of prey (rodents and lagomorphs). Species richness, diversity, and relative abundance of most mammal species was higher in yards and suburban forests than in rural forests. Within a yard, purposeful feeding had the strongest effect on animal relative abundance, with eastern gray squirrels (Sciurus carolinensis) being the most common (32.3 squirrels/day at feeders; 0.55 at control sites; 0.29 in suburban forests; and 0.10 in rural forests). We observed species using (e.g., eating) most yard features, although canids were less likely than other taxa to use resources in yards. The presence of a yard feature did not strongly affect the abundance of species at the control site in the yard, suggesting the influence of these features was highly localized. The relative abundance of predators had a positive association with prey relative abundance, and predators were less common in yards with fences. These results demonstrate that there is high use of anthropogenic resources, especially supplemental feeding by urban wildlife, and this increase in prey species may then attract predators, which supports the hypothesis that use of supplemental food resources explains the abundance of urban wildlife.